Antenna support



Jan. 18, 1966 M. SIJLITEANU ETAL 3,229,941

ANTENNA SUPPORT 2 Sheets-Sheet 1 Filed June 4, 1962 ELEVATION (PITCH)AXIS POINTING (ROLL) AXIS AZI MUTH REFERENCE SERVO PARALLEL T0 ELEVATIONFY. AXIS I FIG. 2

INVENTOR, MENAHEM SULITEANU y WILLIAM R. LA VALLEY Jan. 18, 1966 M.SULITEANU E AL 3,229,941

ANTENNA SUPPORT Filed June 4, 1962 2 Sheets-Sheet 2 INVENTORS, MENAHEMSULITEANU WILLIAM R LA VALLEY.

BYMM? 7 /1. iM L- g ATTORNEY United States Patent 3,229,941 ANTENNASUPPORT Menahem Suliteanu, Palo Alto, and William R. La Valley, LosAltos, Califi, assignors to the United States of America as representedby the Secretary of the Army Filed June 4, 1962, Ser. No. 210,276 4Claims. (Cl. 248-163) The present invention relates to a support and p0-sitioning structure for antennas and the like.

In the utilization of equipments that are used for far distant tracking,the need has arisen for extremely large antennas. Such antennas in turnrequire large pedestal and positioning equipments which use'rotarymotion in one, two, or three planes to provide the necessary degree offreedom. The use of conventional designs makes for extremely large andbulky supports, complexity of drive and control systems and resultanthigh initial and maintenance costs. It has further been found that suchequipments when providing accurate motion around several axes, requireprecision bearings, gears, motors and the like with resultant rise incosts of maintenance. A three axis pedestal and positioning support isrequired to use all three axes to accomplish a search or trackingoperation. As a result such support is confronted with accelerations,inertia forces, etc. in three planes. 'In addition, it will be obviousthat a three channel servo system is required for operating suchequipments. It has often been found that large torsional and bendingmoments are created in pedestals used for supporting conventional, or inspecial instances antennas of over 60 feet diameter. For such largesystems operating in high winds, these moments can be considerable andbecome the limiting factors in the design and manufacture of suchpedestals.

A major consequence of the various short comings, such as indicatedabove, is that available pedestals, as off the shelf or short deliveryitems are limited to antennas of up to about 24 feet in diameter andhaving a restricted performance range. Antenna pedestals which have tobe custom engineered and built, even if conventional designs areutilized, require considerable delivery time because of this complexity,size, weight and precision requirements. In addition large pedestalspost serious transportation problems because of their complexity andsize and possibility of damage to precision bearings and gears.

The primary object of the present invention is to provide a support andpositioning device for an anenna that includes no heavy castings orforgings, no large bearings or gears, and no complex mechanisms.

An important feature of the invention lies in the provision of a supportin which accurate, fast and precise control of the motion of the supportcan be realized.

Another feature of the invention is that in its operation, the antennasupport can be moved from one position to another using angular motionin one plane. In the symmetrical and simplest such motion the antennamount changes in elevation (or its complement the co-elevation, morecommonly called co-altitude, C, having zero value at Zenith) withoutrotation about its pointing axis. Considering only plane geometry thiswould seem to avoid any such rotation; However, in spherical geometry itbecomes apparent that a tilt from Zenith to the Horizon at differentpoints results also in a difierent part of antenna being nearest theground; therefore change in azimuth along the Horizon involves a rollingmotion or rotation about the pointing axis at the tracking rate. Thiscompares favorably to the rotation about pointing axis near Zenith (andNadir) in conventional Az El mounts, which rotation may often be muchfaster than tracking rate and also in a region where target trackingrates themselves are usually faster than near Horizon. However, analysisof possible operation of the present mount below Horizon reveals morerapid rotation, becoming even worse near the Nadir where a conventionalmount would have merely the same problem as at the Zenith; thus thepresent mount may be considered to have traded the pole or Zenithproblem of prior mounts for an increased theoretical Nadir problem, ofno actual importance since tracking rarely extends appreciably beyond ahemisphere anyway. As in other mounts the new mode of operation isapplicable equally to search or tracking.

Ordinary polar spherical coordinates as in prior mounts involve, besidesthe radius, primary and secondary angles, while polar space coordinatesinvolve three equally significant angles (obviously not independentvariables since there is an extra dimension); the very unusual if notentirely new angular coordinates involved in the present mount are bothequally significant, truly x, y in the same sense involved in usualrectangular coordinates. This is particularly apparent near the Zenith;in Horizon and Na-dair regions the rotation becomes more significant.The actual magnitude may be determined by considering the followingrelations:

(a) Azimuth or A1 component dA of tracking rate equals only Az rate dAtimes sin C; that is, Az rate dA equals Az tracking rate dA times Csc C,variable from unity at horizon to infinity at either Zenith or Nadir.

(b) In plane geometry interior polygon angles add to 11 (n2) or 180 fortriangle, 360 for square, etc. If more simply considered by thecomplementary angles or amount of bend at each corner, the total bend Bis 360 for any polygon, including a curve or circle of infinite sidesand corners. Any discrepancy is considered as angular closing error, asin plane surveying. However, in spherical geometry and surveying suchdiscrepancy, known as spherical excesss, above such H (n-2) isrecognized as actually the area in spherical radians; considering thetotal bend angles B this would be an equal deficiency below 2H forspherical area of any shape, or:

A=2IIB Thus, the perimeter of each hemisphere has zero totalbend or theentire 211 deficiency, a lune 180 bend or II deficiency (the remainder311 by changing algebraic sign), etc. The same applies to any areagreater or less than hemisphere (observing signs properly), of whichcircles about the pole are of immediate interest.

(c) Area or surface, S, of such-circles in spherical radians is also:

Thus

B=2II Cos C corresponding to the rotation of an Az El mount antennaabout its pointing axis. This is:

(1) Equal to A2 at Zenith, (2) Zero at Horizon, (3) Opposite to Az atNadair,

This is the combination of the same rotation as a conventional Az Elmount and a rotation opposite in magnitude to the Az, obtained bysubtracting the absolute values, and is:

(1) Zero at Zenith,

(2) Opposite to A2: at Horizon, still of moderate value;

(3) Double and opposite .to Az at Nadir.

(e) Now Combining (a) with (c) and (d), and including tracking rate Azcomponents A, the net rotations are:

2IldR =BdA CscCv=2IIdA CscC Cos C,

(=2IIdA Cot C) for Az El mounts, which is:

(1) Infinity at Zenith, (2) Zero at horizon, (3) Minus infinity atNadir; and

for Anpod mount, which is:

(1) Zero at Zenith;

(2) Opposite. to Az (rate and tracking rate) at horizon;

(3) Minus (double) infinity at Nadir, but in a region rarely used intracking anyway. The two polar problems at Zenith and Nadir of ordinarymount have been both transferred to the Nadir, and a resulting moderaterotation at Horizon does not involve any real problem.

The following illustrative values show the relations between operationof Az El and Anpod mounts. The simple Csc C factor in both varies from 1to the value infinity, which tends to determine the maximum of antennarotation rates. The simple Cos C and fairly simple Cos C-l factors varyover a total range from 1 to 2 including the value zero, which actuallydetermines the minima. The clearly dominant factors of each product andthe products showing problem regions are underlined, while the suitableregions are emphasized by asterisks; the dominance of the Csc C factoris affected yokes. rigidity between the antenna and its supportingstructure.

The ability of the supporting legs of the supporting device to becollapsed, as hereinafter described to less than full extension allowsfor easier storage of the sup-; porting structure. porting structureless subject to wind loads.

The invention can best be understood from the following description tobe read in view of the accompanying drawing in which FIGURE 1 is a viewin perspective of the support and positioning device of our invention asused to support an antenna;

FIGURE 2 is a view in perspective showing details of the construction ofone end of one of the tripod assembly supports; FIG. 3A, B, C, D arepurely diagrammatic views to illustrate successive positions andtherefore the movement involved in tracking.

Referring particularly to FIGURE 1, the antenna support and positioningdevice is designated generally at 11 shown mounted on a base 13. In thespecific embodiment of the invention shown herein at FIGURE 1, thesupport device includes three tripod assembly supports. It is to beunderstood howeverv that three or more such tripod assemblies may beused to support an antenna, and the number of such supports may bevaried dependent upon specific requirements. Since all three tripodassemblies are identical, only one such tripod will be described.

Each tripod assembly includes three extendible and retractible legs15,17, 19. As each leg of the tripod assembly is identical, only oneneed be described. Thus for example leg 17 includes a tubular portion17A and a movable piston-like portion 17B that is slidably engagable inthe tubular portion. The base or lower end of the tubular portion 17Aterminates in a ball which is engagable in a socket on the base 13 toprovide a ball and socket joint 21. By such arrangements the leg 17 ispermitted free motion in any direction as is true of legs 15- and 19. Atits other end each tripod assembly terminates in a triangular shapedframework 23 made of three similar sized arms 23A, 23B and 23C. The armsare slightly spaced from each other and linked by pivot pins, one ofwhich is shown in dotted outline at 25. Pivotally mounted on each one ofthe three pins 25 is the end of y the other factor. one of the pistonlike sections of the legs 15, 17, and 19.

Az El Anpod C Csc C Cos C Use 0 Cos C Cos C-l Use C C 0 (cos 0-1) onm 1. 0 0 w 0. 000 11. 4 11.5 99s 0. 004 11. 5 '-0. 046

*1.0 1.4 .7 -0.3 1.4 '-0.42 *0 1.0 g 1.0 1. 0 1. 0 -1.0 1. 4 7 1."! 1. 42. 38 -11.4 i s 996 1. 996 11 .5 23. m m 1. 0 2. O L on In the 'formsused above only approximate Csc values are needed to observe the trendsin the values at any range of angles, but the difference between Cot andCsc values yields. the same results; at very small angles accuratetables would be needed, or a very close approximation can be usedinstead, either Sin 0/ 2 or (Sin C)/2.

The co altitude component of tracking rate may now be combined todetermine entire motion, only one rotation about the current elevationaxis for such co-altitude, one rotationabout a normal to such axis andactual pointing axis for A2, these two inherent in any tracking, andanother about pointing axis itself for Az, dependent on the particularform of mount.

Still another feature of the invention resides in the use of a supportor mounting ring for the antenna thereby eliminating the need for anysupport brackets, beams or The framework 23 further includes a bearingplate 27 which serves to support a flat plate 29 the bottom end ofwhich. is adapted to rotate in the bearing plate 27.

The plate 29. is further inpivotal engagement with an arm 31 about a pin33 which extends through said arm and plate. Each of the legs can beadjusted in height in unison or separately, as hereinafter described,.sothat a wobble like motion can be imparted thru the framework The use ofsuch mounting ring provides for more This same feature makes suchsupsaid frame. In the same manner the corresponding arms 31 of the othertwo tripod assemblies are also separately joined in bearings to thediscrete apices of the frame 35. Aflixed to the frame 35 is mountingring 37 which serves to'support an antenna 39. In a very general sensethere is a common center at pin 33 from which the leg lengths can bemeasured. The most familiar strong, truly common-center, wide-angle,free-moving joint structure is the universal joint normally used only atnarrow angles as a drive coupling between only two shafts; howeverfurther shafts can be connected at or reasonably close to the samecenter without unduly hampering the freedom of motion. Consideredentirely disconnected from the antenna, equally increasing all leglengths increases tripod height, but if in or near balance as a talltripod, increasing only one leg length mainly controls horizontalposition; if out of balance height may vary directly or inversely withlength, and in widely variable ratio depending on the particular legconsidered and the degree of unbalance. This type of tripod movement hasbeen used previously in 3-dimensional positioning servo-mechanisms asillustrated by Cailloux Patent No. 2,545,258 for microscope slidepositioning, also using an analog tripod input device for control,somewhat similar to the long familiar Z-dimensional Telautograph usedfor writing train arrival times.

Ordinarily the mere change in tripod height is enough to controldirection, particularly in pointing near the Zenith. However, inapproaching the horizon the plane of the antenna control points passesthru a tripod. In the case of a three tripod mount as shown only twopoints would then be controllable or even stable to determine theposition of such plane. If more than three tripods are used the chanceof such loss of control is reduced. In any case separate control of eachleg as noted above avoids the problem, and also can be used to overcomegradual tipping of the entire assembly.

Calculation of the proper leg lengths for each pointing direction is amatter of straightforward solid or spherical trigonometry, complicatedonly because of the several steps of each calculation, and the number ofpossible variables. The same pointing direction can be maintained evenif antenna:

(a) rotates about pointing axis (often changing polarizati-on);

(b) moves in or out on pointing axis (changing range; or

moves up or down with pointing axis (changing parallax).

For maximum simplicity in calculating a single set of leg lengths foreach pointing direction we might assume no variation of these overentire scan. However, the unavoidable roll noted above requiresvariation of (a); again for simplicity we might now assume particularmovement to or from Zenith without change of (a), and about Zenith withsuch a change of (a), conforming to the subtraction of angles noted inthe general description. Variation from such angle could also beobtained by control of leg length, but would complicate control withoutany apparent advantages. This is suflicient for operation, maintainssymmetry of design, etc., but to minimize leg length, height, andwindage, avoid leg interference, provide scan beyond a hemisphere,maintain center of gravity, or for other reasons, some further arbitraryof empirical relation of the declination to variables (b) and (c) may bedesirable. For example, to reduce interference among legs and controlpoints the antenna may lean forward as in FIG. 1; again a center(outside plane of such points) would partly simplify calculations. Oncecalculated and stored in the servo-system the operation would be thesame in any case. To compute or store every possible combination of leglengths for every pointing direction would be hopelessly complex andserve no useful purpose.

system since the tracking hemisphere is divided into a plurality ofanalogous regions corresponding to the order of symmetry, requiringmerely that the calculated leg lengths be assigned to the proper legsfor the region involved. The present system requires a servo havingoutputs corresponding to the number of legs, but the reduction inmaximum antenna velocities and more elfective drive more thancompensates for the number of channels.

As is well-known in structures, for stability the tripod bases should beas wide as possible without interference; the immediately apparentlimiting width involves the same foundation point for adjacent legs. Aneven greater advantage of this arrangement is in simplifying analysis ofthe geometry involved; the three antenna control points become connectedto only three foundation points by six exterior legs, forming sixstructural triangles about the sides, three with one side along thefoundation and three along the antenna, structurally very desirable. Thegeneral form corresponds to a regular octahedron of eight triangularfaces, analogous to the eight spherical triangles used in dividing aterrestrial globe or other sphere. Only four of such triangles would beinvolved in the tracking hemisphere, and its orientation relative to theabove structure is very confusing compared to the situation when fourtripods are used. Use of four tripods is also particularly helpful inanalyzing the tilting motions, both in simplifying movements of parts,permitting designation by compass points as in the tracking hemisphere,and adaptability to the most familiar four lobe tracking control, all infour-fold symmetry; however three lobe control is also rather old. Suchan assembly may be considered as a quasi-regular decahedron of twomutually skewed squares and eight triangles. The operation of a threetripod assembly will thereafter then be easier to explain.

To portray spatial relations in a drawing is difficult at best,particularly with very open structure and when spatial motions areinvolved. Therefore FIG. 3 A, B, C, and D shows diagrammatically onlythe essential elements of a four tripod assembly in several differentpositions. A fixed center in the plane of the antenna control points isassumed merely for simplicity in the geometry. To emphasize the spatialrelations the planes defined by these elements are portrayed as opaquesurfaces, and elements in back are shown dashed. This sketch involvesseveral different types of lines:

(a) The actual legs in heavy lines;

(b) Boundaries of antenna and foundation points in medium lines; and

(c) Certain dot-dashed axes or center lines, dashed projections betweendilferent positional views, and shading to bring out the position of thesurfaces portrayed as opaque, in light lines.

In FIG. 3A the elements are shown symmetrical for Zenith pointing, withN. to S., E. to W., and intermediate center lines or axes of the antennacontrol point plane, either point-to-point or side-to-side; interiorlegs to center of base 'are shown only in this part of the figure. InFIG. 3B the antenna has been tilted to the South horizon, without anychange in the EW axis or its support, the control points showing as asquare. The projection lines from FIGS. 3A to 3B serve to emphasize thatpoints E. and W. need not move for this change in pointing. Inequivalent FIG. 3C tilt to the East horizon is shown, a similarsituation from a difierent viewpoint, the control points appearing in aline representing the edge of a plane. In FIG. 3D tilt to the South Easthorizon is shown, without change in one of the intermediate axes NE. toSW. but changing all the triangles, the square now appearing at about45. In each of FIGS. 3B, C, and D, an axis is shown in the foundationplane and is also in the vertical antenna control point plane(extended); also the compass points marked are all in such plane to helpportray the orientation of the several members. In FIGS. 3B and C thereare re-entrant trihedral corners corresponding to the pointingdirection, and in FIG. 3D the line S. to E. defines a re-entrantdihedral angle, while the antenna controle' square and two triangles arecoplanar. Particularly in FIGS. 3B and it is noted that legs to bothupper and lower corners shorten or lengthen together, contrary to Zenithregion operation; the computed leg lengths would provide for thiseffect.

Now overlooking FIG. 3A, FIGS. 3B, D, C portray progressive positions ofa horizon scan and reveal the rolling action necessary to such scan,accomplished by continuous adjustment of the several legs. Legs to theuppermost control point or point assure proper control, assuming antennaframe rigid, even When legs to lower points may losecontrol. The extrainterior legs to center of base omitted from FIGS. 3B, C, and D avoidrelying on rigidity of antenna frames.

In the case of a triangular top since the axes are pointto-side only,not at right angles, and do not correspond to compass points operationthough equivalent i more difficult to portray. To tilt about one suchaxis assumed as N; to S. the point and center of opposite side arefixed, but the side tilted. To tilt about the center parallel to suchside (normal to such axis or E. to W.) entire side is raised andopposite corner lowered twice as much. Thus the three-fold symmetry ofstructure is unlike the four-fold symmetry of' compass points,complicating analysis of the operation, altho not significantlyaffecting the actual operation.

The raising and lowering of each of the discrete legsof any of thetripod assemblies can be accomplished by any of several'well knownsystems. In the specific embodi merit, as shown in FIGURE 1, use is madeof a hydraulic system utilizing lines 41 connected to appropriatefittings 43. For purposes of programming such hydraulic system blies, inconjunction with the varied pivoting movements.

of the several legs about the pins 25, and the freedom of rotationalmovement permitted by the arms 31 and the plates 27, will cause the ring37 and its associated antenna 39 to move through any desiredgivenpattern from horizon-zenith-horizon sweep to 360 horizon search (at0 elevation).

What is claimed is:

1. An antenna supportcomprising a plurality of, tripod assemblies, eachof said assemblies including three extendible and retractible legshaving discrete rotatable base portions and top ends pivotable in aframework, a plate having one end rotatable in said framework and an armpivotably secured tosaid plate at its other end and rotaw table relativeto a ring support to which said antenna is atfixed.

2. An antenna support comprising a plurality of tripod assemblies, eachof said assemblies including three ex-.

tendible and retractible legs having discrete rotatable base portionsand top ends pivotable in a framework, a plate having one end rotatablein said framework and an arm.

pivotably secured to, said plate at its other end and rotatable relativeto a ring support to which said antenna is aflixed, and means forseparately extending and retracting each of the legs of the varioustripod assemblies.

3. An antenna support comprising. a plurality of identical tripodassemblies each of said assemblies including three extendible andretractible legs that terminate in base portions that are freelyrotatable and wherein the top ends of the three legs of said tripodassembly are discretely and pivotally mounted in a framework, a platefreely rotatable on said framework at one of its ends and having itsother end pivotally mounted in an arm that is free to rotate in a ringsupport to which said antenna is affixed.

4. An antenna support of the kind set forth in claim 3.

and further including means for separately extending and retracting eachof the legs of the various tripod assemblies.

References Cited by the Examiner CLAUDE A.LE1ROY, Primary Examiner.

' N. F. MARTIN, I. H, LACHEEN, Assis tant Examiners.

1. A DEVICE FOR PERFORMING THE DUAL FUNCTION OF BOTH REDUCING THENOMINAL INITIAL SPIN RATE OF A ROTATING BODY TO A DESIGNED FINAL SPINRATE AND COMPENSATING FOR VARIATIONS IN THE INITIAL SPIN RATE OF SAIDROTATING BODY FROM SAID NONIMAL INITIAL SPIN RATE COMPRISING: WEIGHTMEANS; HAVING ONE END ROTATABLE IN SAID FRAMEWORK AND AN ARM PIVOTALLYSECURED TO SAID PLATE AT ITS OTHER END AND ROTA-